Bare glass fibers are substantially smooth rod-like members having surfaces which are highly hydrophilic in nature and thus will not typically exhibit a bonding relationship with elastomeric materials sufficient to provide reinforcement properties thereto. That is, the lack of bonding between the bare glass fibers and the elastomeric material causes the glass fibers and elastomeric material to separate from one another and thus are not useful for the manufacture of glass fiber-reinforced products. It is conventional therefore to apply a thin layer of a size composition to the surfaces of the bare glass fibers which is compatible with and serves to improve the bonding relationship between the glass fibers and the elastomeric material.
The thin layer of size composition serves an additional beneficial function. During processing of the glass fibers into a form suitable for use as reinforcement for elastomeric products, the fibers are exposed to abrasive contact with the structural components utilized during processing. The size composition layer therefore also serves to protect the underlying bare glass fiber from abrasive damage which could otherwise occur during processing.
Glass fibers therefore are typically sized as formed, collected into a strand and the strand is then wound around a take-up bobbin to form a substantially cylindrical package (conventionally termed a "yarn package"). The yarn package is then air dried or subjected to elevated temperatures so as to dry the size composition applied to the surfaces of the plural glass fibers forming the strand. In this regard, reference is made to U.S. Pat. No. 3,816,235 which is incorporated expressly hereinto.
The dried and sized strand is then usually unwound from the yarn package and brought into contact with an impregnant solution of resorcinol-formaldehyde resin in combination with various latexes compatible with the size composition and the elastomeric material. The impregnated strand is again dried so as to cure and set the impregnant on the external surface of the glass strand to ensure that the individual sized glass fibers of the strand are adhered one to another. Subsequent twisting of the cured impregnated strands produces a glass fiber suitable for subsequent forming into cloth, rope, cord or the like to reinforce elastomeric products.
Prior to actual use, however, the impregnated glass strands are typically subjected to storage and/or shipping. The impregnated glass strands are therefore potentially exposed to ambient conditions which could deleteriously affect their properties (such as tensile strength) to such a degree that their use as a reinforcing medium for elastomeric products would be seriously impaired. The size and impregnant system of the present invention promotes the durability of glass strands coated therewith by maintaining the durability (i.e., minimizing tensile strength loss) thereof when subjected to potentially harmful ambient conditions. As used herein, the term "durability" is understood to mean the percent loss in tensile strength when an impregnated glass fiber is exposed to an environment of 125.degree. F. at 90% relative humidity for a period of two weeks. It has been discovered that particularly favorable durability properties for impregnated glass fibers can be achieved utilizing sequentially applied size and impregnant compositions as disclosed herein. Particularly, tensile losses of less than about 10% are achieved when glass fibers are sequentially sized and impregnated with the compositions of this invention.
A further aspect of the present invention resides in the discovery that addition of a pyrrolidone-containing polymer to the size composition substantially prevents fraying of glass fibers at the ends of the yarn package. Since the turns of the glass strands at the ends of the yarn package are not supported by adjacent strand turns, fraying at the ends of the yarn package is sometimes observed. As used herein, the term "fraying" is meant to refer to a quantity of individual fibers in the strand which break and separate from the strand. Fraying of the glass strand at the ends of the yarn package is disadvantageous as breakage of a portion of the individual fibers in the strand will obviously cause a loss in strength to such a degree that the strand (or at least that portion of the strand where fraying has occurred) may not be usable as reinforcement for elastomeric products. The size composition of the present invention solves the fraying problem described above by the addition of a water soluble pyrrolidone-containing polymer which, upon heat curing, migrates to the exterior portions of the yarn package including the ends thereof to form a protective film over the individual glass fibers of the strand which substantially prevents fraying.
According to this invention therefore, there is provided a glass fiber having a first resinous coating formed by drying an aqueous size composition of the hydrolysis product of a copolymer of a vinyl aromatic monomer and maleic anhydride and a glass fiber anchoring agent in the form of an organo silicon compound. Preferably a sufficient amount of a pyrrolidone-containing polymer is present in the size composition to form a protective film on the coated surface of the glass fiber to prevent "fraying".
The sized glass fiber is then coated with a an aqueous composition comprising a vinylpyridine terpolymer, a blend of emulsifiable mineral oils, silica derivatives and esters, a recorcinol-formaldehyde resin, a polybutadiene latex and wax emulsion wherein the vinylpyridine terpolymer and polybutadiene latex are each emulsified with a synthetic anionic surfactant having sulfate, sulfonate or sulfosuccinate groups.
Any suitable glass fiber is usable with the size and impregnant compositions of the present invention. The term "glass fibers" as used herein shall mean fibers formed by attenuation of one or more streams of molten glass and to strands formed when such glass fiber filaments are gathered together in forming. The term shall also mean yarns and cords formed by plying and/or twisting a multiplicity of strands together and to woven and non-woven fabrics which are formed of such glass fiber strands, yarns or cords. Preferably, the size and impregnant compositions of the present invention are usable with E-type fibers having a diameter in the range of from about 0.35 to about 0.50 mil.
The resins employed in the practice of this invention are commercially available in solutions which can be simply blended with other components in the preparation of the compositions embodying the features of the present invention.